Vitreous enameling



Patented Mar. 14,

vr'rREoUs ENAMELING Charles J. Kinzie and Donald S. Hake, Niagara Falls, N. Y., assignors to The Titanium Alloy Manufacturing Company, New York, N. Y., a corporation oi Maine No Drawing, Original application July 2a, 1937,

Serial No. 156,137. Divided and this application March is, 1940, Serial No. 324,736

(Cl. met-4a) 6 Claims.

This invention relates tonew and improyed opaciflers, and to vitreous enamelscontaining such opacifiers. More particularly, it relates to a new and improved zirconium'oxide opacifier.

This application is a division of our copending application Serial No. 156,137, now Patent No.

2,194,426 issued March 19, 1940.

Zirconium oxide has been extensively used as an opacifier in the art of enameling. Inone well known procedure a frit formula i prepared and then smelted to a homogeneous melt, whereuponit is poured into water to quench and produce the frit. The fritthus produced is then milled with other enamel ingredients, including an opacifier, to form a slip, which is coated on: a suitable base, such as sheet iron, and fired to form an enamel. Both zirconium oxide and tin oxide have been used as opacifiers in these enamels, the latter generally being able to-produce the same opacity with slightly smaller quantities compound and a carbon compound, the carbon compound being evolved in the form of gaseouscarbon gas in' contact with a flux. Although the carbon may be present as some other colorless compound of carbon, we are led to believe that it does contain adsorbed C0 throughextensive test made on' the product, as fully described in our aforesaid copending application, now Patent No. 2,194,426. I The presence of (302 may explain the high index of refraction noted-for this prodnot, and may also explain the low density (38 and than the former. However, due to the relatively higher cost of tin oxide, zirconium oxide has been extensively used in the slightly larger quantitles necessary to secure the desired opacity.

In accordance with the present invention it hasrbeen discoveredv that a certain novel zir-' conium oxide product has produced opacity results which are superior to those secured with tin oxide, even when used in considerably smaller quantities. This product comprises a zirconium bon dioxide suitable-for this purpose is that described and claimed in our-aforementioned co-- pending application, now Patent No. 2,194,426.. This may be described asbeing a crystalline ZrOz of high birefringenceIwith-an index of refraction higher than that of baddeleyite, namely, above 2124. The crystals are in the form of. thin plates 34 /2 pounds per cubic foot in two examples) as compared with other zirconium oxide products 1'10 pounds per cubic foot for electrically fused zirconia, and 145 pounds per cubic foot for the synthetic. baddeleyite of U. S. Patent No. 2,072,889) The above density figures are for the products after fine wet milling, which of course is necessary when employing them as enamel opacifiers.

The method of preparing this material andthe apparatus used therefor is fully described in our aforesaid copending application; now Patent No. 2,194,426. Basically, it comprises the formation of 'a-zirconium-oxygen-carbon intermediate in the electric furnace, and the subsequent oxidation of this compound in thin layers, such as of the order of 1; inch thick, at a temperature of apbecomes so high due to heat given off during oxidation that the propertie of the product are altered.

In accordance with the oonium oxide product containing adsorbed CO:

. is added .to a suitable hit at the mill. When such a product was so added 6% at the'mill along.

- with 6% enamelers clay and V49; of magnesium which are longer than wide and also thinner than I 7 their width, and 'whose dimensions are in the range mainly from 1 to 15 microns long, from 0.5 to 8 microns wide, and 0.4 micron to 1 micron thick. This material is additionally characterized as being white of a high order at a magnification of v of the enamel (which is a powerful flux). Such result was undoubtedly due to'the liberation of the adsorbed gas, or to the decomposition of the herein referred to colorless carbon compounds to form colorless gaseous carbon compounds which evolved within the viscous enamel atrelatively gush temperatures (say i500 F) and 'soare present invention, a zir- I entrapped therein with the formation of a matrix of vitreous enamel in which are a multitude of gas pockets, or perhaps better described as-bubbies. We also found that the opacity of this enamel was considerabl higher than that of one from the same frit with 6% mill added tin oxide, and that a relatively small percentage of this new zirconium oxide was capable of producing an unheard-of degree of opacity for such small mill.

addition. To; illustrate our discovery we offer the following experiments and tests.

An enamel frit was prepared by mixing a batch of the following ingredients, all parts by weight This mix was smelted to a homogeneous melt,

poured into water to quench and produce the frit,

and dried. l parts of the above frit, 6 parts of enamelers clay, 0.25 part-of magnesium car-. bonate, and a varying quantity of opacifier were accurately weighed into porcelain jar mills-containing porcelain balls. About 40 parts of water were added to each charge, which was then milled to a fineness of 12'grams residue on a' 200 mesh sieve from a 100 cc. sample slip. The enameling -was done on pieces of sheet enameling iron 6" x 4" size first enameled with a dark ground coat on both sides; the cover coat enamel under test was then applied in two coats. The first coat was first dried and fir'ed for 2 /2 minutes at 1520 F., cooled, and thenanothercoat applied, dried and fired. at l520 If. for 2 minutes. The cover coat was applied in both coats to one side only of the 6" x 4" piece. The total weight of cover-coat enamel was kept within the tolerance 11.90 to 12.10 grams per 6" x 4'! surface. The

opacity orrefiectance was then determined by means of a reflectance. meter.

Except for the kind and amount of the opacifier, all examples were prepared exactly the same. The following table will list the .opacifier additions and the reflectance results. Opacifier X is a zirconium oxide containing adsorbed CO3, prepared in accordance with our aforesaid copending application, now Patent No. 2,194,426,

' and shows the following analysis:

' Per cent Zirconium oxide .(ZlO2) 97.85 Titanium oxide (T102) 0.10 to nil Silicon oxide (S102) 0.10tonil Silicon carbide (SiC) Trace to nil Carbon dioxide (CO2) 1.64 r

, Iron oxide (Fe2O3) 0.01

Others 0.30

I Opaeifier Y is a typical tin oxide used for opacitying enamels. Opacifler Z is a roasted product prepared according .to Example B of U; S. Patent No. 2,102,627.

Parts oland Enamel test letter Enamel A, as will beobserved, contains no mill addition opacifier and has a reflectance of 60. In enamel 0,-0.10 part tin oxide has practically no effect in increasing the reflectance, while as noted in enamel H, 0.50.part tin oxide only inincreased the reflectance from 60 of A to 61.9. On the other hand zirconium oxide containing adsorbed CO2 imparted a regular increase in opacity.. Based on these results it may be stated that in these lower percentages the zirconium oxide produces from three to four times as much increase in opacity as does tin oxide, Thus in enamel B, 0.10 part of opacifier X produced practically as much opacity as compared with 0.50 parts tin oxide in enamel H, while 0.20 part of opacifier X in enamel D produced considerably more opacity as compared with the tin oxide of enamel H. Again enamel G, with 0.50 part of this zirconium oxide, has a higher opacity reading than did enamel K containing two parts by weight of tin oxide. Enamel O and P show that a high grade zirconium oxide opacifier, like tin oxide, has none of the properties of the ZrOz containing adsorbed CO2.

When zirconium oxide containing adsorbed carbon dioxide is used in amounts much above one part by weight to 100 parts'by weight 01 frit,

the enamel is definitely expanded and the surface, although having agood lustre, is of a texture entirely different as compared with that of a smooth enamel. The 2 parts and 3 parts by weight addition of opacifier X produced a surface with considerable lustre, but it had a decidedly wrinkled texture. The addition of 1 part of this zirconiumoxide produced an enamel of smooth texture, but with somewhat less lustre as compared with enamel A, while 0.50 parts of opacifier X produced an enamel having a good lustre.

As a mill addition opacifier in vitreous enameling, therefore, zirconium oxide containing adsorbed carbondioxide possesses an opacifying power hitherto unknown, since relatively small amounts added at the mill produce opacity to a degree hitherto unknown for any mill addition material. Where high lustre smooth texture enamels are desired, the amount used should be kept below the point where the texture and lustre are materially affected, namely, in-amounts .70.

of 1 part or less by weight to parts frit. The textures produced by higher percentages may be of interest as special vitreous enamel finishes.

In the above description and examples, when part:i are mentioned, parts by weight are under.- s o We claim as our invention:

1. A white vitreous enamel containing as an opaquing agent a minor quantity of a zirconium' oxide compound having an adsorbed carbon di-'- oxide content .in which carbon dioxide evolvedv during firing produces opacity.

2. A white vitreous enamel containing as an opaquingagent a minor quantity of a zirconium oxid compound of low density and high purity compound of low density and high purity having an adsorbed carbon dioxide content in which carbon dioxide evolved during firing produces opacity.

5. A method. of iorming white opaque enamelscomprising milling a irit with water and a minor quantity of an opaquing agent comprising a zirconium oxide compound of low density and high purity having an adsorbed carbon dioxide content, applying' the milled slip thus formed to a base, drying, and firing at sucha temperature as to cause said opaquing agent to react with the remaining enamel ingredients and form minute bubbles of carbon dioxide throughout said 10 enamel.

6.; A method of forming white opaque enamels comprising milling a frit with water and 0 .1% to 1%, based on the weight of the frit, of an ,opaquing agent comprising a zirconium oxide com- 5 pound of low density and high purity having an adsorbed carbon dioxide content, applying the milled slip thus formed to a base, drying, and firing atsuch atemperature as to cause said opaquing agent to react with the remaining 20 enamel ingredients and form minute bubbles of carbon dioxide throughout said enamel.

CHARLES J. DONALD s. mum 

